Management of Primary Malignant Tumors of the Osseous Spine

Classification

Less than 5% of the 2500 primary malignant bone tumors that are found each year in the United States occur in the spine. For that reason, few centers can achieve a critical level of experience in the management of these tumors. The terminology used to describe these tumors has tended to vary considerably from one region to the next. In addition, there were no staging systems that helped one decide which type of surgery to perform. All of these reasons entered into our decision to help develop the Weinstein, Boriani, Biagini (WBB) surgical staging system. This system is designed to unify the ways tumors are described in order to facilitate communication between physicians. Once a common descriptive language is accepted, it also helps to facilitate research efforts. The WBB system helps guide the surgeon with regard to what type of resection is possible.

The WBB system divides the axial presentation of the vertebrae involved with tumor into 12 zones similar to a clock face ( Fig. 177.1 ). Position number 1 begins at the left half of the spinous process and position 12 ends at the right half of the spinous process. Zones 4 and 9 are particularly important to know because they define, respectively, the left and the right pedicle. Vertebrectomy with adequate surgical margins depends upon one of these two zones to be free of tumor. The vertebra is further divided into radial zones. The radial zones define the depth of tumor invasion. For instance, zone A represents a soft tissue mass extending beyond the confines of the bony cortex. Zone B describes tumor within the superficial bony vertebrae, and zone C defines tumor within the deep bony vertebrae. Zone D describes epidural tumor involvement and zone E is intradural. It is also important to describe the longitudinal extent of the tumor.

As an example, a tumor of a lumbar vertebra involving the left pedicle and the vertebral body, extending in the psoas and the epidural space can be described based on the distribution within the WBB staging system as involving zones 4 through 8 with extension into zones A and D.

This system has been submitted to intra- and interobserver reliability assessment by a group of spine tumor experts

Indications for En Bloc Resection

The goal of en bloc surgery is to remove the whole tumor with a continuous shell of normal tissue, the margin. Often the tissues surrounding spine tumors are functionally very important and even unresectable. Sometimes nerve root resection leads to significant motor deficit; sometimes a situation arises where a meaningful surgical margin is not possible without transection of the dura or even the spinal cord. These options should be first weighted considering the long-term outcome of oncologically appropriate surgery versus intralesional surgery in each specific condition. ^, A 2009 systematic review of the literature offered evidence (low quality due to the small number of cases reported) that for thoracic and lumbar spine aggressive osteoblastoma, giant cell tumor (Enneking 3), en bloc resection—when anatomically feasible—can be recommended to minimize the risk of local recurrence. En bloc resection should be undertaken for chordoma and chondrosarcoma of the spine, provided wide or marginal margins can be achieved, because it is related to a reduced rate of local control and mortality. In osteosarcomas and Ewing sarcomas of the spine, en bloc resection is associated with better local control and overall survival if associated with a full course of chemotherapy.

The margins are a valid predictor of local and systemic prognosis, ^{, , , ,} but the possibility to compensate intentional margin transgression with multimodal treatments should be carefully considered. The option of relevant functional sacrifices to target better systemic prognosis must be discussed with the patient. For some patients, the idea of paralysis is not worth considering. Conversely, others might wish to accept paralysis in exchange for a possible cure. This is clearly a decision that only the patient should make in conjunction with the counsel of the surgeon. En bloc resections are sometimes proposed also in the treatment of bone metastases in the spine. This indication is open to discussion because the criterion to plan the treatment of metastatic disease is palliation, and risk-to-benefit ratio should always be carefully considered. However, when local control is the primary issue—in solitary metastases from clear cell tumor or colon carcinoma—en bloc resection, if feasible with acceptable risk, may be an option. Bilsky et al., however, in a 2009 systematic literature review, concluded that stereotactic radiosurgery is better than en bloc resection in the treatment of solitary metastases from clear cell carcinoma without epidural extension.

Finally, the specific morbidity of en bloc resections should always be carefully considered.

Preoperative Planning

The WBB system was designed to plan surgery. Preoperative MRI and CT scan are required to provide the details of tumor extension and normal tissue reactions necessary for the WBB staging system. Because the goal of surgery is to obtain a negative margin, the surgical planning should include in the specimen at least one sector and one layer outside the tumor border. In particular, the en bloc resection of the vertebral body will result in a tumor-free margin when the tumor spares at least one pedicle (zones 4 or 9). Extension into zone D can preclude one from obtaining a negative margin unless a layer of healthy tissue (pseudocapsule) exists between the tumor and the dura. It is not always possible to know this until the time of surgery. Close attention should be paid to zone A extension. The anterior approach should be directed toward the side with maximum zone A involvement to allow best visualization. In addition to these, one must pay close attention to the cephalocaudal extent of the tumor. This will help determine whether the transverse cuts should be made through a disc or vertebral body. If a foramen is involved, then the nerve root in that foramen needs to be taken with the tumor to obtain a tumor-free margin. It may be necessary to remove a nerve root to facilitate tumor exposure even on the nontumor side of the vertebra. This is easily accepted as connected with low morbidity in the thoracic spine.

It is imperative to plan ahead when en bloc resection is entertained. Sometimes a multidisciplinary team of surgeons must be assembled to perform this procedure. This team may include a thoracic surgeon, vascular surgeon, and/or abdominal surgeon, among others. Skilled anesthesia is critical, and postoperative intensive care should be anticipated. Blood products must be at the ready in case rapid infusion is necessary to counteract hypovolemia.

According to the WBB planning system, four general types of en bloc resection in the thoracic and lumbar spine can be identified:

• A posterior resection ( Fig. 177.2A ) for posteriorly occurring tumor (see Fig. 177.2B )

  

• A posterior-only approach ( Fig. 177.3A ) for vertebral body tumors not expanding in layer A (see Fig. 177.3B )

  

• A staged approach (see Fig. 177.5A ) for vertebral body tumors expanding anteriorly in layer A (see Fig. 177.5B )

  

• A posterior-only or staged sagittal resection (see Fig. 177.6A ) for eccentrically located tumors (see Fig. 177.6B )

  

En bloc excision from a posterior-only approach is possible for vertebral body or eccentric tumors, but it provides an adequate oncologic margin only for tumors without extension into zone A. For all tumors that extend into zone A we recommend a staged posterior and anterior procedure, the anterior release being the first step. It is our opinion that the staged approaches are safer and allow the best oncologic margins.

The techniques of en bloc resections are based on experience collected since 1991, applying and modifying the original techniques by Stener and Roy-Camille. ^,